Comparator



Oct 16, 1945. K. R. woon ETAL 2,387,2B0

GOMPARATOR Filed June 8, 1942 4 Sheets-Sheet 1 R7 Vd' f v 6 2,35 /f W y?3 s/f'/ s V JM s\\ erzne 472 I/VoaoZ QW Carl W 17ml' @CL 16, K R WOOD ETAL 2,387,21@

COMPARATOR Filed June 8, 1942 4 Sheets-Sheet 2 Oct. i6, 1945. K. R. woonETAL.

COMPARATOR 4 Sheets-Sheet 3 Filed June 8, 1942 Q 0 j u d g y 7 1305002 y35% y JV n,. a y o ag w F HWMHH E .Oct 16, 1945. K. R. WOOD ET AL Zm@GOMPARATOR Filed June 8, 1942 4 Sheets-Sheet 4 Patented Oct. 16, 1945COMPARATOR Kenneth R. Wood and Carl W. Ahmer, Chicago,

Ill., assignors to Union Special Machine Company, Chicago, Ill., acorporation of Illinois Application June 8, 1942, Serial No. 446,226

2 Claims.

An object of the above invention is to provide an instrument forcomparing the enlarged shadow of the contour of an object with anequally enlarged standard contour drawn or otherwise imposed on atranslucent screen to determine the degree of accuracy existing in theobject to be tested, which instrument is so constructed as to permiteconomical manufacture and in which the parts are so arranged as not torequire precise limits in the dimensions of its component parts.

Another object of the invention is to provide, in a comparator of thereflecting type, a mirror mounting so disposed that the mirror can beadjusted toward and from the viewing end of the projector to effect avariation in the degree of magnification without changing the positionupon the viewing screen of a selected part of the enlarged shadow.

Still another object of the invention is to pro-V vide a. comparator ofthe above type having a viewing screen which is disposed closer to'theuser than the Work piece being compared and a screen-protecting hoodwhich partially extends over the Work piece so that at least a partialshielding of the screen from the light projected on the work piece isobtained.

A still further object is the construction of a comparator having theabove advantages and which in addition is light in weight and readilyportable.

Still another object is so to mount the comparator per se on a base asto enable the viewing end to be quickly adjustable to differentelevations to accommodate either standing or seated users of differentheights.

One manner in which the above-mentioned and other objects may beattained is disclosed in the attached drawings taken together with thefollowing descrpition thereof; it being understood that equivalents andminor variations will be apparent to those skilled in the art.

In the drawings:

Figure I is a side elevation partly in section,

Figure II is a corresponding view on a large scale, with parts brokenaway to show details of the assembly,

Figure III is a rear view of the projector,

Figure IV is a top plan, partly'in section, taken on the line IV-IV ofFigure II,

Figure V is an exploded view of the chart securing means,

Figure VI is a front elevation of a preferred form of supportingcarriage,

Figure VII is a sectional view taken on the line VII-VII of Figure V,

Figure VIII is a top view of the stage assembly,

Figure IX is a sectional side elevation of the stage assembly,

Figure X is a sectional viewtaken onthe line X-X of Figure IX, and YFigure XI is a bottom view of the mirrorsupporting head on line XI--XIof Figure II.

As shown in Figure I, the structure includes a general support GS towhich is hinged a comparator body or hood H. A work stage WS supportsthe piece of Work W in the path of a beam of light from a projector PJ.This piece of work W is located at the focal plane of the microscopesystem MM which projects the image of the work'as a beam of light,downwardly in the hood H and against a reflecting mirror RM, whichreflects the beam upwardly and onto a translucent viewing screen VSlocated at the top of the hood H. The axis ray LB-I of the beam from themicroscope MM encounters the reflecting mirror RM and produces thereflected ray LB-Z which thus forms the axis of the reected beam whichis passed on to the viewing screen VS. It

is preferred to adjust the parts so that this reflected ray LB-2encounters the Viewing screen VS at its center of eiective area, whichthus becomes a reference point which is invariable durg ing furtheradjustment of the system. To secure this invariance, as will be .set outin detail hereinafter, the reflecting mirror RM is mounted so that itcan be moved linearly along the bisector AA of the angle between the tworays LB-I and LB-2.

In th drawings, the device is shown with the viewing screen VSsubstantially horizontal, and with the hood located below this viewingscreen; and the following description will, therefore, refer to theupperend of the hood as that shown near the top of the drawings, and thefront of the apparatus will be .described as the portion toward the leftin Figures I and II; but it will be understood that the screen may beviewed from other directions if so desired, and that the hood may beadjusted in angle so that the rays LB-I and LB-2 are approximatelyhorizontal, particularly when thedevice is to be employed upon a tableand by a seated operator.

The comparator body comprises a base member I which may, if desired, bea wood plank. Mounted on this base are side members 2 and- 2a and a rearmember 3, which in conjunction with the base member l form alight-excluding hood which is closed at its lower end by an end memberbase member I.

4 to which the adjacent ends of the side and rear members are attached.The hood has a top wall B which is located below the upper end of theThebase member extends beyond the top wall l to provide a support for asource of light which may. for example, be in the form of an ordinarycommercial type of projector PJ. The top wall i is apertured to receivea system of magnifying lenses or microscope MM which is secured inposition by a set screw l. Above the top wall I, the rear part of thehood projects upwardly beyond the top wall l. A viewing screen VS ismounted at the extreme front end of the hood in a manner which will behereinafter more particularly described. A closing wall la extends fromthe top wall l to the screen VS, to form with the walls I, 2, 2a, 3,4and C a substantially light-tight hood. In front of the projectingportion of the hood the base member I has an aperture and carries a workholding stage WS extending through the aperture and having a work holder|08 which is adjustable in the directions of lines normal to each otherand to the axis of the light beam projected by the projector PJ and alsoadjustable along a line parallel to said axis.

The optical systemcomprises the projector PJ which projects light upon apiece of work mounted in the work support WS, the projecting lens ormicroscope MM which is focused on the part of the piece of work whichlies at the focal plane and delivers a beam of light, having an axialray L'B-I, into incidence upon the reiiecting mirror RM, with areflected beam, having an axial ray LB-2, which is projected upwardly.again and upon the viewing screen VS, encountering the same at a rightangle. The angle of incidence of the axial ray LB-I and the angle ofreflection of the axial ray LB-2 with the surface of the reflectingmirror RM are identical by the laws of optics: and the bisector AA ofthe anle between the rays LB-I and LB-2 is in the plane o f the incidentand reflected rays and is normal to the surface of the reflecting mirrorRM. To afford a maximum use of the available field, the projector PJ andthe microscope MM are coaxially mounted, and a critical point of a workpiece is preferably held by the work holder at the common axis, i. e. inline with the ray LB--I; and likewise the point of incidence of thereflected ray LB-2 upon the viewing screen VS is at the center of thisscreen. Therefore, when this condition has been established by theconstruction and adjustment of the parts, the shadowed image of theaforesaid critical point will appear at the center of the viewing screenVS.

Mounted for endwise movement in a socket or holder II carried on theoutside of the end member 4 is a rod I2 which is confined to axialmovement in said holder along a line which is coincident with thebisector of the angle formed by the intersection of a line normal to thesurface of the screen VS at the center thereof and the 4axis of thelight beam projected by the projector PJ. This may as illustrated beconveniently attained bytapering the upper end of the base member I toprovide a surface I a upon which the projector is attached to secure thelight beam and the base at the intended` angle of incidence of the lightbeam LB-I upon the mirror, thereby permitting the end 'member 4 to bemounted at a right angle to the base, thus eliminating difculties informing and securing the end member at another angle. Within the hood,the rod i2 is provided with an integral T-shaped head I3 which has anupwardly projecting stud I4. Clamped to this stud by a clamp screw Il isa rearwardly extending member Il in the rear end of which is clamped astud II which extends laterally and thence rearwardly from the member Iland which at its end is provided with a ball head bored to receive astud Il projecting downwardly from a mirror supporting plate I! andwhich is clamped in said ball head by set screws 2l. Threaded into theheads of lthe T-head Il (Figures II and XI) are bolts 2|, 2l havingheads which engage the back of the mirror assembly I! to impart theretothe proper angular adjustment in assembly for positioning the mirror RM.Lock nuts 22, 22 -are provided to secure the bolts 2|, 2I whenadjustment has been secured. 'I'he outer end of the rod I2 is internallythreaded to be engaged by an adjusting screw 22 having a grooved head 24which is engaged by a dowel pin 25 in the holder I I so that turning ofthescrew 23 will effect bodily endwise movement of the rod I2 and themirror system carried thereby. When the desired adjustment has beenachieved, the r'od I2 locked in place by the set screw 28. I

The socket II is preferably protected against contact with the oor orother objects by a guard 4a which is secured to the end wall 4. and hasan aperture 4b to permit access to the head 24 of the adjusting screw23.

In devices of this character it is desirable that the magnificationobtained be of a predetermined ratio and that that ratio be accuratelyachieved, so that the shadow of a standard device will accurately matchthe prepared comparison chart. This may be done by making parts whichenter into the magnification with extreme and costly accuracy or byforming some part of the apparatus for adjustability whereby the ratioof magnication can be accurately determined during 40 the assembly ofthe device. In the present invention the mirror is mounted foradjustment along the bisector line AA. In assembly, the mirror is lrstadjusted by bolts I2 for angular position until the shadow image of thesaid criticalpoint of the work piece falls at the center of the viewingscreen VS and then, by movement along the axial line AA of its mounting,the degree of magniiication of the shadow image projected on the screenis varied until the desired ratio is established. It will be notedparticularly that if tbe mirror were movable along a line notsubstantially the bisector of the angle between the incident andreflected beams endwise adjustment of the reiiector would result in arelative upward or downward shift of the projected image, necessitatinga further angular adjustment of the mirror, requiring again an endwiseadjustment until the desired magniiication and position of image on thescreen is obtained. -With the aforesaid primary adjustment of angularposition, the shadow image of the critical point remains relatively xedupon the viewing screen VS, and the size of the image increases ordecreases in the radial directions away from this point. This. aspreviously pointed out, is avoided by making the several mirroradjustments independent of each other, with one affecting the positiononly of the image and the other affecting the size only of the image.

The base member I at its rear or lower end is connected by a hinge 21 tothe support GS having a platform 28 which is provided with a blfurcatedupstanding bracket 29 between the adjacent faces of which is received asliding plate 30 Secured to the underside of the base I. The plate readyportability of the entire 30 is further provided with a slot 3l which isarcuately concentric with the axis of the hinge 21 and through whichpasses a. clamp bolt 32 carried in the bracket 29.

If desired the support GS may be arrangedfor device, one sucharrangement -being illustrated. As shown, the platform 28 at its rearend is provided with a single leg 33 and at its forward end with a pairof casters 36. It will be apparent that it is necessary only to tilt theapparatus toward the user, thus lifting the leg 33 from the door, andthen the apparatus is free to be wheeled wherever desired. It willfurther be apparent that, by providing the platform with three points ofsupport, the device can be used anywhere without regard for a possibleunevenness of the floor.

A rockable light shield 35 may be provided at the upper end of the hood,to cut off lateral illumination fromA the viewing screen VS; this shieldis shown as mounted by a hinge 3d and held in position by clampingscrews 3l.

The projector PJ (Figures I and 1I) includes a housing l0 in lwhich ismounted a suitable lamp il and a condensing lens system 52. Themicroscope MM includes a series of suitable lenses (i3 mounted in .atubular holder it which is externally provided with a coarse-pitchthread d engaged in the top wall 6 and held in an adjusted position bythe locking screw d. By this means the lens system may be properlylocated in assembly so that the focal plane will be in a proper positionrelative to the work holding stage. Once this is established there is nofurther need to change the location of the microscope MM except thatwhich is incidental to the removal for the purpose of cleaning thelenses. Within the hood H, the microscope carries a shield and diaphragmil which cuts down the field projected by the lenses to eliminateundesirable color fringes from the projected images and to assure theinterior of the hood against the presence of light other than that inthe focused beam.

The viewing screen VS (Figure VII) comprises a sheet of plain glass d8which rests in rebates on a frame composed of the members dta and servesto seal the end of the hood, and a suitable translucent screen on whichthe shadow image of the object is projected. This screen may have chartoutlines drawn thereon for use as a standard for or as a gauge to checkthe accuracy of the part being tested. This screen may be formed of apair of plain glass plates 9, it with a sheet of translucent material E@bearing suitable chart lines cemented between them or may be a singlesheet of stili' transparent material such as glass frosted on one sideand with suitable chart lines or other indicia marked or etched at theother side. Many other methods of preparing such comparison elements orstencils will suggest themselves to those skilled in the art.

The essential thing is that the chart must be quickly mountable anddemountable and must be so mounted as to be angularly and laterallyshiftable to facilitate alignment with the shadow cast by a standardwork piece held on the stage WS. To this end, (Figures II, V and VII)the the rear edge of the hood above the glass it carries achart-supporting bar l aixed thereto by screws 52. 52. This bar 5l has arebate at its edge, provided with a centr-a1 raised chartsupportingledge 53 which is opposed by a clamp member 5t which is held in place bya clamp screw 55 threaded into a collar` 5B in the bar 5l. At eitherside of the ledge 53 the rebate has .Y supporting clearance spaces 5l,5l and the walls upstanding from these parts of the rebate are directedat angles to the front edge of the bar to permit anguiar adjustment ofthe chart. At the front edge oi the hood, above the glass 48, is asecond chartbar 58 affixed to the end of the hood by screws 59, 59. Thismember does not extend beyond the chart and is provided withtwo chartsupporting ledges G0, Bil. Pivotally mounted on the bar 58 by means of ashoulder screw 8l is a rocking bar 62 provided with chart holding clampsB3, 63 and clamp screws 6d, 6d which oppose the ledges Bt, 60. Therocking bar 62 is further provided with a slot through which extends athumb screw 66 which is threaded into the bar 58 and serves to clamp thebar in any desired angular position. In setting up a chart, the chart isrst set on the supporting ledges with the clamps loosely engaging -thechart. Next a standard Work piece is placed in a suitable work holderand, by adjustment of the work-holding stage WS, is brought intoposition to produce a sharp image at the approximate desired locationupon the viewing screen VS. Finally, the chart is positioned angularlyby tilting the bar 62 and laterally by the lateral bodily movement ofthe chart or the work piece until the proper relationship of chart linesand shadow is established, after which the chart clamp screws 55 and 6dand the thumb screw 5t are tightened, thus holding the chart in thedesired position. Thereafter other work pieces can be placed in the workholder and their correctness can be judged by the relation of theirprojected shadows to the chart.

The work-holding stage WS comprises a support plate el iixed to theunderside of the base l by screws 68. Fixed to the support plate 6l is adepending member @t formed with a pair of parallel transverse V-grooves"it, l@ adapted to guide a pair of round bars ll, ll, held by screws l2in a pair of grooves it, 'l formed in a sliding member lli and held incontact with the member 69 by a clamping stud l5 threaded into themember 'lli and extending through a slot 15a in the member E@ to theopposite side thereof where it carries a thumb nut l@ by which themembers ld and 69 may be clamped in adjusted positions. Adjustment in adirection parallel to the bars 'll is effected by a screw ll threadedinto the enlarged central portion i8 of the stud l5; the screw il isprovided with a hand wheel 'i9 and has a reduced diameter portion dwhich is engaged by a split bearing di on the member 69, which bearingincludes the separable bearing cap t2 secured by screws 83.

To provide for adjustment ofthe work stage (Figures II, IV, E and X)toward and from the base l, the member lt is further provided with apair of parallel spaced V-grooves 3d, Bil at right angles to theV-grooves l0, l@ and in which a pair of round bars d5, 8E are secured byscrews 85. Sliding on these bars is a member 31 provided with matchingV-grooves 88, 88, which member is held in contact with the bars 85, B bya stud 89 threaded into the member 1B and which extends through a slot@d in the member 8l and exteriorly thereof carries a thumb nut 9i.Adjustment of the member 8l in a direction parallel to the bars d5, 85,is achieved by a screw 92 threaded into the enlarged center portion 93oi the stud 89, which screw is provided with a hand wheel M and has areduced diameter portion @E which is journaled in a split bearing 93formed in the member 80 and including the removable bearing cap 31 andscrews 98.

'I'he member 81 at its inner end is provided with a forwardly extendingportion 99 which receives a. pair of parallel round bars |00, which aresecured by screws |0| in the V-grooves |02, |02, which extend parallelto the light beam and at right angles to the V-grooves 10, I0 and 84,84. These bars engage the V-grooves |03, |03 formed in the face of thesliding block |04 of work-holdlng stage WS so that the block |04 slidesfreely along these bars in a direction parallel with the axis of theincident light beam. 'Threaded into sliding block |04is a stud |05 whichprojects through a slot |06 in the portion 99 of the member 00 andexteiorly thereof carries a thumb nut |01 by which the stage can belocked in adjusted position. If desired, this adjustment may be effectedby a hand screw structure similar to that by which the adjustments alongbars 1|, 1| and 85, 85 are effected, but experience has indicated thatsuch is not required since the purpose of this adjustment is merely tobring the part being inspected into a sharp focus: and by proper designof the work-holding fixtures, such adjustments are unnecessary.

For the purpose of illustrating a. typical use of this comparator, thereis shown (Figures II and IV) a sub-base |08 mounted on the upper slidingblock for supporting a work-holding fixture |09 which is secured thereonby pinch levers I0, H0 pivoted at and actuated by thumb screws H2, ||2.The work holder |09 is formed with spaced arms I3, H3, each having aprojecting dowel pin ||4 corresponding to calibrated apertures in thework pieces to be inspected, and on which a work piece W is mounted.

In the illustrated use, the location of the edges IIB, il'l, ||0 and ||9of the flat work piece relative to the holes through which the dowelpins ||4 pass is being checked and the front surface of the work pieceis held at the focal plane by the work stage. The image will be reectedin inverted form on the screen and will be checked against thecorresponding lines Ilia, lila, ||8a and ||9a on the chart, (Figure IV).

Other types of work holders may be constructed and employed inaccordance with the shape of the work piece and the portion thereofwhich is to be inspected, being provided with devices against whichportions of the work pieces abut for locating the successive work piecesin identical positions with the desired parts of the work positioned atthe focal plane and in proper relation for projection of their shadowsupon the viewing screen VS.

The operation of the instrument is simple. When constructed andinitially adjusted so that the focal plane, microscope and mirror arecoordinated to present an image of proper ratio and in proper positionupon the viewing screen VS, the work stage WS can be fitted with variouswork holders in accordance with the work piece to be inspected.

The operator energizes the lamp bulb 4l for illumination and places awork piece in the work holder, by introducing it as with any toolfixture. Its image is thereupon projected onto the viewing screen VS andmay be compared, at the magnification afforded, with the chart. Errorsin the work piece will appear, in the illustrated form, by the presenceof shadow at one or the other side of the true position represented bythe lines "8a-I |0a'of Figure IV.

After the ilrst work piece has been inspected,

it is removed. and another work piece substituted.

It will be noted that this inspection is accomplished. after initialadjustment ofthe comparator as a whole and of the work stage WS for theparticular piece of work, without any other operation than the manualinsertion and removal of work pieces and visual inspection of theirimages; and hence the operations can be performed by a relativelyunskilled inspector.

It is obvious that the invention is not limited to the particular formor details of construction, butmay be practiced in many ways within thescope of the appended claims.

We claim:

1. An optical comparator having a housing. a viewing screen xed acrossan opening of the housing, a lamp fixed on the housing, a work holderand a mount on the housing therefor, a projecting lens fixedly mountedon the housing for projecting thereinto a light beam from the lamp, amirror in the housing for reilecting theA light beam toward the screen,a work mount including means for adjusting the work piece until aselected part thereof is at the axial light ray through the projectinglens, together with a mirror-supporting assembly arranged on the housingopposite the opening and including a member adjustable for determiningthe scale of enlargement produced by the comparator by bodily movementtoward and from the lens and screen along a line lying within the angleformed at the mirror by the incident axial light ray from the projectinglens and the corresponding reilected axial ray, said member having auniversal joint connected to the mirror and devices for moving themirror about axes of said universal joint at angles to the directions ofsaid axial rays and eective for maintaining the mirror in an angularposition in which the angle between the incident and reflected axiallight rays is bisected by the line of said bodily movement of the saidmember, a chart at the screen having lines indicating the position andsize of the image of a standard piece of work, and means for shiftingthe chart laterally and angularly until the reflected axial ray fallsupon the part of the chart corresponding to said selected part of thestandard work piece and the said chart lines coincide with correspondingparts of the image of a standard piece of Work, whereby the bodilymovement of the adjusted mirror is eiective to correlate the size of thesaid standard image with the chart lines.

2. An optical comparator comprising a. supporting member, a source oflight mounted adjacent one end of said member'for projecting a lightbeam along the length of said member, a panel fixedly projecting fromthe supporting member intermediate its ends and having an aperture, alens fixed on the panel for focusing the light beam through saidaperture, housing walls fastened to said member and panel for providinga substantially light-tight chamber having one end extended beyond thepanel and closely adjacent thereto, whereby a selected point of the Workcan be brought to a predetermined part of the light beam, a screeniixedly mounted across an opening on the extended end of the chamber,means for providing at the screen a representation of the standardarticle for comparison, said representation being of a predeterminedenlarged size and in predetermined orientation upon the screen with thepoint corresponding to said selected part of this work occupying apredetermined location within the area of the screen, a mirror in thechamber for reecting the said iight beam toward the screen, supportingmeans for the mirror including a device whereby the mirror is guided forbodily movement toward and from the lens and screen along a line lyingbetween the incident and reflected rays from said selected part, andalso including means ior'angularly adjusting the mirror relative to thedirection of said bodily movement into an angular position on saiddevice at which the line of said bodily movement lies along the bisectorof the angle between the incident and reected rays from said selectedpart, whereby the mirror may be moved along said line of bodily movementfor adjusting the size of the projected shadow outline of the work uponthe screen without changing the screen position of said reflected rayfrom said selected part. l

KENNETH R. WOOD. CARL W. AHMER.

